I am installing dual CHT temps on cyl #1 & 2 on my 85HP today, figured it would be easier to control the cooling balance side to side.
Presentl, use duct tape, more on colder days, less warmer.
Doesn't seem to accurate when all you went by was oil temp, & I always wondered if you could be over heating one side & cold on the other?
Hence the dual CHTs

With the probes under the spark plug, what temp range should I be aiming for

Well, if you're installing more than one CHT probe, put four of them in there, and install a four cylinder gauge. Just instrumenting two cylinders isn't very helpful, and the idea that one on each side of the engine will tell you what's actually going on is mistaken.

In factory single probe installations, the factory figures out which cylinder runs the hottest, and they install the probe on that cylinder. More often than not, it's a rear cylinder, as opposed to a front cylinder, but I've flown engines (my O 360 on a C170 was one) that ran one of the front cylinders hottest. Go figure.

So, unless you know which cylinder actually runs hottest in your installation (and that will vary with different aircraft models/cowlings/mods/etc) then ANY cht installation is probably misleading at best.

You could experiment with running the probe in one cylinder, then switching it, till you find the hottest cylinder. But, one of the problems is that the hottest cylinder may and often does change with different operating modes.

I'd spend some time and a little money getting my engine baffles as near to perfect as possible, and not worry too much about CHT. Very few of the airplanes that were built with C-85s were equipped with CHT gauges.....go figure.

MTV

You could experiment with running the probe in one cylinder, then switching it, till you find the hottest cylinder. But, one of the problems is that the hottest cylinder may and often does change with different operating modes.

Well that is something I could experiment with.

I still think a temp probe is worthwhile, for instance, I hear about shock cooling warnings when descending at 0*F, probes would certainly let you know if & to what extreme temps are changing.

But I still would like to know approx what range head temps should run...200F...400F...600F ?

380 degrees.

Good article here: http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning198162-1.html

Do your best to keep them under 400F, especially in the climb. In cruise I doubt you will have to worry much about them.

FWIW the CHT is redlined at 525 on my O-470, using a sparkplug gasket type probe. I switched to a bayonet type probe when I replaced the gauge recently, the TCDS says 460 redline with that.

Every engine is different.....information from an O-470 may or may not be even close to a C-85.

Try looking at the Type Certificate Data sheet for the C-85 Continental engine (I'm assuming that's the engine you're talking about??). Here's a link to the TCDS: http://www.airweb.faa.gov/Regulatory_an ... v%2018.pdf

Try bookmarking the TCDS web link. There is a LOT of ACCURATE and USEFUL information there, and it only takes a minute or two to find it, as opposed to all kinds of "sorta" information by those of us who peruse these web forums....

MTV

mtv wrote:Every engine is different.....information from an O-470 may or may not be even close to a C-85.

Try looking at the Type Certificate Data sheet for the C-85 Continental engine (I'm assuming that's the engine you're talking about??). Here's a link to the TCDS: http://www.airweb.faa.gov/Regulatory_an ... v%2018.pdf

Try bookmarking the TCDS web link. There is a LOT of ACCURATE and USEFUL information there, and it only takes a minute or two to find it, as opposed to all kinds of "sorta" information by those of us who peruse these web forums....

MTV

Well, I fall into the "sorta" camp that if you're going multi-point CHT instead of single point, make it all 4 on a 4 cylinder engine. On my O-360, the back two run markedly hotter than the front two during climb-out (about 430F), but they all pretty much even out in cruise (380-390). I don't notice the front ones getting particularly colder than the back ones on descent. The right front runs a little cooler in cruise than the left front, but not a lot. The back two are pretty even with one another. Leaning varies a lot on which one peaks first, although most often it's the left rear.

So if I had a Continental 85 hp engine and wanted to install a CHT indicator, it'd probably be a single point on the cylinder that Continental says should run hottest. But since most low powered aircraft engines run pretty consistently, neither too hot nor too cool, I'd more likely just rely on the oil temp gauge and forget CHTs altogether.

Cary

Cary wrote:

mtv wrote:Every engine is different.....information from an O-470 may or may not be even close to a C-85.

Try looking at the Type Certificate Data sheet for the C-85 Continental engine (I'm assuming that's the engine you're talking about??). Here's a link to the TCDS: http://www.airweb.faa.gov/Regulatory_an ... v%2018.pdf

Try bookmarking the TCDS web link. There is a LOT of ACCURATE and USEFUL information there, and it only takes a minute or two to find it, as opposed to all kinds of "sorta" information by those of us who peruse these web forums....

MTV

Well, I fall into the "sorta" camp that if you're going multi-point CHT instead of single point, make it all 4 on a 4 cylinder engine. On my O-360, the back two run markedly hotter than the front two during climb-out (about 430F), but they all pretty much even out in cruise (380-390). I don't notice the front ones getting particularly colder than the back ones on descent. The right front runs a little cooler in cruise than the left front, but not a lot. The back two are pretty even with one another. Leaning varies a lot on which one peaks first, although most often it's the left rear.

So if I had a Continental 85 hp engine and wanted to install a CHT indicator, it'd probably be a single point on the cylinder that Continental says should run hottest. But since most low powered aircraft engines run pretty consistently, neither too hot nor too cool, I'd more likely just rely on the oil temp gauge and forget CHTs altogether.

Cary

Precisely.

MTV

I don't give a fig for what the manufacturers say, I set the (engine monitor) alarm for 380 F and call 400 red line on my Scout. I am fiddling when 370 approaches to get the temp to drop. This could include less throttle and more RPM, adding more fuel or even subtracting fuel. It is amazing how quick CHT's will drop when lean of peak. A bit of carby heat will also drop temps.

I seldom go over 6000' but I do note it runs hotter at altitude. Sea level temps generally run around 350 F

Over 400 and the strength of aluminium castings is greatly reduced.

You need a monitor that does all cylinders.

Good article here: http://www.avweb.com/news/savvyaviator/ ... 162-1.html

Thank you for that link MTV, I now have a starting point.

NOTE 1. Maximum permissible cylinder head, barrel and oil inlet temperature are as follows (oil pressure limits 30 to 40p.s.i.):


Head Barrel Oil Inlet
C75 Series 550°F. 300°F. 225°F.
C85 Series 540°F 300°F. 22

The maximum temperatures listed are indeed far higher than most of us want (or will for that matter) to see in our engines.

The good news with these little Continentals and the installations they're typically found in run waaaaay cooler than these temps.

In fact, if anything these engines run cool as opposed to hot.

FWIW

MTV